Electronic component and panel and method for the production thereof

ABSTRACT

The invention relates to an electronic component and a panel, the electronic component having a semiconductor chip with a wiring board and a plastic package. The plastic package is made up of two layers of plastic package molding compound arranged one on top of the other. These layers are created with the aid of a printing operation under normal atmosphere.

BACKGROUND

The invention relates to an electronic component and a panel and to amethod for producing the same.

Electronic components that have a semiconductor chip and a wiring boardarranged on the upper side of the semiconductor chip already form withthese components the package of the electronic component. All that isnecessary for this purpose is to apply the wiring board to thesemiconductor chip with the aid of a double-sided adhesive film. Thewiring board carries the external contacts and a patterned metal coatingof wiring leads, which lead from the macroscopic output contacts to themicroscopically small contact areas of the upper side of thesemiconductor chip in a bonding channel of the wiring board. In thisconnection, microscopically small is understood as meaning a dimensionwhich lies in the micrometer range, and can consequently only bemeasured with the aid of an optical microscope, whereas the macroscopicexternal contacts are understood as meaning dimensions which can beperceived with the naked eye and can be measured with simpleinstruments.

To protect the sensitive semiconductor chip, the upper side of thewiring board, which is connected to the semiconductor chip, mayadditionally carry a plastic package molding compound. This plasticpackage molding compound may either protect the edges of thesemiconductor chip or completely surround the semiconductor chip, asknown from the patent U.S. Pat. No. 6,048,755 for BGA packages (ballgrid array packages). For applying such protective plastic packagemolding compounds to the upper side of the wiring board and forencapsulating the semiconductor chip, either high-pressureinjection-molding processes may be used, operating at working pressuresof over 100 bar in order to avoid inclusions of air bubbles in theplastic package molding compound, or vacuum printing installations maybe used, to ensure back-side protection of the semiconductor chipswithout air bubbles. Since, in vacuum printing installations, theapplication or printing of the back sides of the wiring board and thefilling of the intermediate spaces between the semiconductor chips isperformed under a vacuum, with these installations there is no risk ofthe inclusion of air bubbles since there is no air in the vacuum.

Both methods of protecting the back sides of the semiconductor chips,that is methods which operate under a vacuum or at high pressure, arecostly, but result in the semiconductor chip being encapsulated by asingle costly method step. In addition, both methods take up relativelylarge intermediate spaces between a number of semiconductor chips to bepacked simultaneously in plastic molding compound, in order to ensurethat the plastic package molding compound is reliably introduced aroundthe semiconductor chips without air bubbles. Attempts to providelow-cost methods which permit the plastic package molding compound to beprinted onto the back sides and the edge sides of the semiconductorchips in normal air fail because of the inclusions of air bubbles, inparticular if the intermediate spaces between a number of semiconductorchips to be packed in plastic package molding compound become evercloser because of increasing density per unit area being worked.

SUMMARY

One embodiment of the invention provides an electronic component and apanel and also a method for producing them. The component has astructure that makes it possible to apply a plastic package moldingcompound with which the inclusion of air bubbles is reduced. At the sametime, the production costs are reduced.

According to one embodiment of the invention, an electronic componentwith a semiconductor chip, a wiring board and a plastic package isprovided. The plastic package has two plastic package molding compoundsarranged one on top of the other. One of the plastic package moldingcompounds forms a first layer, which completely encloses at least theedge regions of the semiconductor chip, and the other of the plasticpackage molding compounds forms a second layer, which is arranged on theback side of the semiconductor chip.

No mechanically and hygroscopically unstable limit forms at thetransition from one plastic molding compound to the other, especiallysince the properties of the plastic package molding compound in thefirst layer can be adapted to the complex edge region structure of thesemiconductor chip and the second plastic package molding compound isadapted to the requirements of application over the surface area on theback side of the semiconductor chips. By adaptation of the properties ofthe plastic package molding compound in the first layer, evencomplicated structures, as occur in the edge region of semiconductorchips, can be provided with plastic without any bubbles. Since aboundary phase is not perceptible with the naked eye, but only apparentunder microscopic examination, the external appearance of the electroniccomponent remains unchanged for the user market, although thiselectronic component is produced at lower cost by much less expensivemethods on account of the combination of the plastic package moldingcompounds and the matching of their properties to one another.

In one embodiment of the invention, the plastic package molding compoundof the first layer has in the uncrosslinked state a lower viscosity thanthe second layer. This has the advantage that the first, low-viscositylayer can be introduced even into narrow intermediate spaces betweensemiconductor chips of a closely packed leadframe or panel with manycomponent positions in an extremely confined space by a printingtechnique and without any bubbles.

Since, when the leadframe or panel is divided up into individualcomponents, the sawing track runs within the intermediate spaces, anedge protection for the semiconductor chips is consequently alreadyproduced with the first layer that is introduced into the intermediatespaces. Furthermore, it is ensured that the formation of air bubbles isminimized in these edge regions on account of the low viscosity of thefirst layer of plastic package molding compound in the uncrosslinkedstate. This first layer of the plastic package molding compound with lowviscosity in the uncrosslinked state is so liquid that it wets the edgesof the semiconductor chips and, in the case of small intermediate spacesbetween two semiconductor chips, can be introduced into the intermediatespace without any bubbles on account of capillary forces.

In addition, this first layer of the plastic package molding compoundwith low viscosity in the uncrosslinked state has a surface that isextremely smooth and planar.

Consequently, an almost planar boundary phase can form between thelow-viscosity first layer and a high-viscosity second layer. Since allthe intermediate spaces between the semiconductor chips on a wiringboard are already filled by the first, low-viscosity layer, anddifferences in height are leveled out, when the second, high-viscositylayer is applied in the uncrosslinked state, an extremely planar andsmooth boundary layer can be produced between the two layers without theformation of air inclusions.

In a further embodiment of the invention, the viscosities of the firstand second layers in the uncrosslinked state differ in such a way thatthe viscosity of the first layer is lower by at least an order ofmagnitude than the viscosity of the second layer. On account of thisclear difference in viscosity, the first layer is so liquid that it canpenetrate without any problem and without air bubbles into extremelynarrow intermediate spaces between semiconductor chips, and canconsequently wet the edge regions of the semiconductor chips with anyplastic molding compound and protect them in the crosslinked state.

A further aspect of the invention relates to a panel with a number ofcomponent positions for electronic components. The panel has aleadframe, which has in each component position a bonding channelopening which is filled with a plastic covering compound. The panel hason the opposite side from the bonding channel a number of spaced-apartsemiconductor chips in the component positions. The intermediate spacesof these semiconductor chips are filled with a first layer of plasticpackage molding compound and the back sides of these semiconductor chipsare covered with a second layer of plastic package molding compound. Inthis case, the plastic package molding compound of the first layer inthe uncrosslinked state differs from the plastic package moldingcompound of the second layer in that the first layer in theuncrosslinked state has a lower viscosity than the second layer.

This construction of the panel allows it to be cast or printed for anumber of components simultaneously with a first layer of lowerviscosity and then the back sides of the semiconductor chips can becovered with a high-viscosity layer completely and without air bubbles,and at the same time with dimensional stability. Only after both layershave been applied in an uncrosslinked state can there follow atemperature step, in which both plastic package molding compounds, bothof the first layer and of the second layer, crosslink while maintaininga boundary phase between the two layers.

This boundary phase is demonstrably evident in microscopically smallregions, both on the panel and on the individual electronic component,from micrographs of the plastic package molding compound. In thisconnection, microscopically small is understood as meaning a scale whichlies in the micrometer range, dimensions only being ascertainable underan optical microscope.

The viscosities of the first layer and of the second layer of the paneldiffer by at least an order of magnitude, so that the first layer canfill the intermediate spaces between the semiconductor chips of a panelwithout any bubbles even when there is extremely dense packing of thepanel. With a high-viscosity second layer, which then finds a relativelyplanar boundary area or surface, a further and dimensionally stableplastic package molding compound can be applied by a printing techniquewithout any air bubbles. The advantage of such a panel is that, for anumber of components at the same time, a plastic package moldingcompound comprises two components, that is a low-viscosity component anda high-viscosity component, which form a plastic package without any airbubbles.

One method for producing the panel from a leadframe for a number ofelectronic components in corresponding component positions withsemiconductor chip, which are encapsulated by two layers of a plasticpackage molding compound, has the following method steps:

-   -   provision of a leadframe with a number of component positions        which have a bonding channel opening at their center,    -   application of a double-sided adhesive film with a bonding        channel opening in the component positions,    -   application of semiconductor chips with their active upper sides        to the double-sided adhesive film,    -   introduction of bonding connections in every bonding channel for        electrically connecting contact areas of the semiconductor chip        to external contacts on the underside of the leadframe,    -   filling of the bonding channel with a plastic covering compound,    -   printing of a first layer of low-viscosity plastic package        molding compound onto the back sides of the semiconductor chips        for filling the intermediate spaces between the semiconductor        chips on the leadframe,    -   printing on of a second layer of high-viscosity plastic package        molding compound for covering the back sides of the        semiconductor chips,    -   curing of the plastic package molding compound to form a closed        upper side of the panel with the formation of a boundary phase,    -   application of external contacts to the underside of the panel.

With this method, many steps on the way to producing an electroniccomponent can be carried out in parallel for a number of electroniccomponents. In addition, with this method the intermediate spacesbetween the semiconductor chips, and consequently the packing density ofthe semiconductor chips on the leadframe of the panel, can be made to beextremely close, since no evacuation of the intermediate spaces betweenthe semiconductor chips is required, but rather the low-viscositycomponent of the first layer in the uncured state can fill theintermediate spaces between the semiconductor chips without any bubblesby means of capillary action.

Furthermore, with the first low-viscosity layer, an extremely planarboundary phase can be built up between the first layer and the secondlayer, so that when the high-viscosity layer is applied no air bubblesare introduced into the boundary layer between the low-viscosity layerand the high-viscosity layer. The curing of the two plastic packagemolding compounds of the first layer and of the second layer can takeplace simultaneously in an annealing oven, so that a closed smooth andplanar upper side of the panel is produced. Application of externalcontacts to the underside of the panel on each of the external contactareas of the underside of the leadframe provides that a high number ofexternal contacts can be soldered in on the underside of the leadframeat the same time and by one step.

In an example of how the method of the invention is carried out, theprinting on of the first and second layers of low-viscosity andhigh-viscosity plastic package molding compound takes place by means ofscreen printing. For this purpose, a screen which has an opening of thesame size as the entire panel is placed onto the leadframe and alow-viscosity plastic package molding compound is introduced anddistributed with the aid of a spatula. In this case, the plastic packagemolding compound is introduced into the intermediate spaces between thesemiconductor chips partly by means of capillary forces, without theformation of air bubble inclusions.

Both when printing on the first layer of low-viscosity plastic packagemolding compound and when printing on the second layer of high-viscosityplastic package molding compound, a spatula is used, and is pressed ontothe printing screen under pressure in order to produce the most uniformand planar outer surfaces possible of the electronic component or outersurfaces of the package of the electronic component.

In a further example of how the method is carried out, the second layerof plastic package molding compound, which is applied to the back sidesof the semiconductor chips, may be applied with the same printing screenas the first layer of plastic package molding compound. These methodsteps create a panel for a number of electronic components, which has acomplete plastic package of plastic package molding compound on oneside, this package comprising two layers lying one on top of the otherwhich are introduced in an advantageous way without any air bubbles,because the first layer consists of a low-viscosity plastic packagematerial and the second layer is made up of a high-viscosity material.The high-viscosity covering of the back sides of the electronicsemiconductor chips at the same time brings about the effect that theplanar surface which is produced by a screen during the printingoperation can be retained in a dimensionally stable form during theentire process phases, in particular also during the curing process.

A method for producing an electronic component from the panel merely hasone further step to follow, that is dividing up the panel intoindividual electronic components. For this purpose, a saw is used todivide up the panel through the intermediate spaces, which are in themeantime filled with low-viscosity plastic, so that, if the externalcontacts have already been applied to the panel in advance, a completeelectronic component is provided, for attachment to a higher-levelcircuit structure such as a printed circuit board. One advantage of thismethod is that it is possible to dispense with expensive vacuum printinginstallations and expensive high-pressure injection-moldinginstallations for the method according to the invention.

To sum up, it can be stated that the filling of the leadframe with aplastic package molding compound to form a panel for a number ofelectronic components can take place by coating or printing thelower-lying regions between the chips with a low-viscosity andnon-bubble-forming plastic package molding compound and subsequentlyoverprinting the entire panel with a high-viscosity plastic. Thisoverprinting makes it possible for the individual semiconductor chipswithin the panel to be encapsulated without any bubbles.

The low-viscosity encapsulating compound or plastic package moldingcompound that is applied first may already be cured, or else beoverprinted with a high-viscosity encapsulating compound while in thenot yet cured state. The method has the consequence that it is possibleto dispense with the vacuum process steps that are otherwise required inthe case of vacuum printing. Furthermore, for methods which providedegassing of the plastic package molding compound, the slower multipleprinting and the slower degassing in a vacuum can be replaced by thefaster printing processes with low-viscosity material and withsubsequent high-viscosity material.

The spacing limitation required for the evacuation of the intermediatespaces that has to be observed in the case of the vacuum printing methodis also no longer needed, so that a certain gain in surface area is madepossible by closer packing of the leadframe with semiconductor chips.The sinking of the encapsulating compound when it is applied by only onemethod step can also be prevented by this two-stage method. Oneembodiment of the invention utilizes a combination of low-viscosity andhigh-viscosity plastic package molding compounds in order to ensurebubble-free printing of plastic packages on semiconductor chips by meansof a multistage process.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of this specification. The drawings illustrate theembodiments of the present invention and together with the descriptionserve to explain the principles of the invention. Other embodiments ofthe present invention and many of the intended advantages of the presentinvention will be readily appreciated as they become better understoodby reference to the following detailed description.

The elements of the drawings are not necessarily to scale relative toeach other. Like reference numerals designate corresponding similarparts.

FIG. 1 illustrates a schematic cross-sectional view of an electroniccomponent of a component position of a panel of an embodiment of theinvention.

FIG. 2 illustrates a basic diagram of a device for applying a firstlayer of a plastic package molding compound for a panel.

FIG. 3 illustrates a basic diagram of a device for applying a secondlayer of a plastic package molding compound for a panel.

FIG. 4 illustrates an extract from a flow diagram for the step-by-stepproduction of a plastic package molding compound on a panel for a numberof electronic components.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments of the present invention can be positioned ina number of different orientations, the directional terminology is usedfor purposes of illustration and is in no way limiting. It is to beunderstood that other embodiments may be utilized and structural orlogical changes may be made without departing from the scope of thepresent invention. The following detailed description, therefore, is notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims.

FIG. 1 illustrates a schematic cross-sectional view of an electroniccomponent 1 of a component position 18 of a panel 36 of an embodiment ofthe invention. The reference numeral 2 identifies a semiconductor chip,which is connected by its active upper side 27 on a wiring board 3 bymeans of a double-sided adhesive film 26. The reference numeral 4identifies a plastic package, which is made up of a first layer 5 of aplastic package molding compound 23 and a second layer 6 of a plasticpackage molding compound 23. Between the plastic package moldingcompounds 23, or between the first and second layers 5 and 6, thereforms a boundary phase 13, which is demonstrably evident under amicroscope both for the electronic component 1 and for the panel 36.

The reference numeral 7 identifies the outer sides of the plasticpackage 4, which in the case of this embodiment of the invention, whichconstructs a plastic package 4 by means of a printing technique, doesnot substantially differ significantly from plastic packages 4 that havebeen produced by means of high-pressure injection-molding processes orby means of vacuum printing processes.

In the case of the high-pressure process, such a high pressure isexerted on the plastic package molding compound that air bubbles arepressed out of the assembly, whereas in the case of the vacuum printingprocess air bubbles cannot occur for the very reason that the entireprinting is carried out in a vacuum chamber.

The reference numerals 8 and 9 identify the edge regions of thesemiconductor chip 2, which are enclosed at least by the first layer 5of plastic package molding compound 23. The reference numeral 10identifies the back side of the semiconductor chips 2 or thesemiconductor chip 2, which is completely covered with plastic packagemolding compound 23, the greatest proportion of this plastic packagemolding compound 23 being provided by a high-viscosity plastic moldingcompound, which is applied in a second step to the back sides 10 of thesemiconductor chips 2, to form a second layer 6. The reference numeral11 identifies a closed upper side of the panel 36, which issubstantially the upper side of the plastic package molding compound 23of the second layer 6.

With the reference numeral 12, the intermediate spaces between thesemiconductor chips 2 of a panel 36 are identified. These intermediatespaces 12 may be made extremely narrow, since the low-viscosity plasticpackage molding compound 23 in the uncrosslinked state can penetrateinto very narrow intermediate spaces 12 by means of capillary action. Inthis way, the packing density of the semiconductor chips 2 on aleadframe 20 can be increased and improved. The reference numeral 13identifies the boundary phase, already mentioned above, between thefirst, low-viscosity layer 5 and the second, high-viscosity layer 6 ofplastic package molding compound 23.

Arranged on the underside 21 of the leadframe 20, opposite from theplastic package molding compound 23, is a bonding opening 14 for abonding channel 15. This bonding channel 15 allows the microscopicallysmall contact areas 34 of the semiconductor chip 2 to be connected tothe macroscopic external contacts 30 on the wiring board 3. For thispurpose, bonding connections 16 are arranged between the contact areas34 of the semiconductor chip 2 and the wiring leads 19 on the undersideof the leadframe 20. The wiring leads 19 extend from the bonding channel15 to external contact areas 30 on the underside of the wiring board 3.These external contact areas 30 carry external contacts 22, which arearranged on the external contact areas 30 on the underside 21 of theleadframe 20.

At the transitions of the bonding connections 16 to the wiring leads 19,they have bonding ends or bonding fingers. These bonding ends may beimproved by a coating. Since the wiring leads 19 substantially comprisea copper layer, a copper-diffusion-inhibiting metal and a precious metalarranged on top of the latter may be provided for the improvement. Thecopper-diffusion-inhibiting metal may be nickel or alloys of the same,since copper cannot diffuse through this nickel layer. The preciousmetal layer may consist of gold, silver or alloys of the same andprovides frictionless bonding. By applying a flux to the externalcontact areas 30, external contacts can also be soldered onto theexternal contact areas 30.

The sensitive bonding connections 16 may be protected by filling thebonding channel 15 with a plastic covering compound 17. In this case,the height of the plastic covering compound 17 is less than the heightby which the external contacts protrude from the underside of the wiringboard 3 or the underside 21 of the leadframe 20. The leadframe 20itself, which has a number of component positions 18, comprises a coreplate 32, which for its part consists of glass fiber reinforced epoxyresin.

As illustrated in FIG. 1, the electronic component 1 has a bubble-freeplastic package molding compound 23 on the semiconductor chips 2, sincean inclusion of air bubbles is prevented in principle by the multistageapplication of the plastic package molding compound 23 in the form of afirst, low-viscosity package molding compound and a high-viscositypackage molding compound applied on top of the latter.

In one embodiment, the difference in viscosity between the first layer 5of plastic package molding compound 23 and the second layer 6 of plasticpackage molding compound 23 is at least an order of magnitude. Thisensures that the first layer 5 of plastic package molding compound 23can be introduced into the intermediate spaces 12 between thesemiconductor chips 2 without bubbles, so that the edge regions 8 and 9of the semiconductor chip 2 are protected by a plastic package moldingcompound 23 surrounding them. The second, high-viscosity layer 6substantially covers the back sides 10 of the semiconductor chips 2, sothat complete encapsulation of the semiconductor chips 2 is ensured bythis embodiment of the invention.

FIG. 2 illustrates a basic diagram of a device for applying a firstlayer 5 of a plastic package molding compound 23 to a panel 36.Components with the same functions as in FIG. 1 are identified by thesame reference numerals and are not explained separately.

The device, as illustrated in principle in FIG. 2, has a screen 25,which leaves a screen opening 37 over the semiconductor chips 2. Aspatula 24 is moved in the direction B over the screen 25 and therebyspreads a first, low-viscosity plastic package molding compound onto theopening 37 in the screen. This low-viscosity material distributes itselfin the intermediate spaces 12 between the semiconductor chips 2. Sincethese intermediate spaces 12 can be extremely small, the filling of theintermediate spaces may, given an appropriately low viscosity, beassisted by capillary action, by which the first plastic package moldingcompound 23 penetrates into the intermediate spaces between thesemiconductor chips 2 without any bubbles.

At the same time, a pressure is exerted in the direction of the arrow Aon the spatula 24, which is arranged in a mount 35, in order that theopening 37 in the screen 25 can be filled completely with the plasticpackage molding compound of the first layer. At the same time, part ofthe back sides 10 of the semiconductor chips 2 may also be printed withthe low-viscosity plastic package molding compound 23.

FIG. 3 illustrates a basic diagram of a device for applying a secondlayer 6 of a plastic package molding compound 23 for a panel 36.Components with the same functions as in the preceding figures areidentified by the same reference numerals and are not explainedseparately.

When this device is used, the intermediate spaces 12 are already filledand a spatula 24 is then moved in the direction of the arrow B, at thesame time pushing a bead of high-viscosity plastic package moldingcompound 23 in front of it, and consequently printing a covering ontothe back sides 10 of the semiconductor chips 2 in the componentpositions 18. This high-viscosity plastic package molding compound 23can be applied without any bubbles, because the first layer forms anextremely planar surface as a boundary phase.

FIG. 4 illustrates an extract from a flow diagram for producing aplastic package molding compound 23 on a panel 36 for a number ofelectronic components 1. The flow diagram comprises in the first stagethe printing of the opening in the screen, and consequently the printingof the semiconductor chips with a low-viscosity plastic package moldingcompound. This low-viscosity plastic package material will become lodgedin the intermediate spaces between the semiconductor chips of a panel,without air bubble inclusions occurring.

In the second stage, there is then carried out a second printingoperation, in which a high-viscosity plastic package molding compound ispressed into the opening of the screen with the aid of the spatula,while applying a pressure in the direction of the arrow A to the deviceillustrated in FIG. 3.

In the third stage, the plastic is cured with the aid of thermal steps.For this purpose, the low-viscosity, first layer may have already beencured in advance, so that in the third stage the high-viscositycomponent is crosslinked.

The fourth stage comprises the dividing up of the panel into individualelectronic components.

1-12. (canceled)
 13. An electronic component comprising: a semiconductorchip having edge regions and a back side; a wiring board; and a plasticpackage having first and second plastic package molding compoundsarranged one on top of the other, wherein the first plastic packagemolding compound completely encloses at least the edge regions of thesemiconductor chip as a first layer and the second plastic packagemolding compound is arranged on the back side of the semiconductor chipas a second layer.
 14. The electronic component of claim 13, wherein thefirst plastic package molding compound of the first layer in anuncrosslinked state has a lower viscosity than the second layer.
 15. Theelectronic component of claim 13, wherein the viscosities of the firstand second layers in an uncrosslinked state differ in such a way thatthe viscosity of the first layer is lower by at least an order ofmagnitude than the viscosity of the second layer.
 16. The electroniccomponent of claim 13, wherein the first plastic package moldingcompound is adapted to application at the edge regions of thesemiconductor chip.
 17. The electronic component of claim 13, whereinthe second plastic package molding compound is adapted to applicationover the back side of the semiconductor chip.
 18. The electroniccomponent of claim 13, wherein the first and second layers are producedby means of high-pressure injection-molding processes.
 19. Theelectronic component of claim 13, wherein the first and second layersare produced by means of vacuum printing processes.
 20. A panel with anumber of component positions for electronic components comprising: aleadframe which has in each component position a bonding channel openingthat is filled with a plastic covering compound; and a number ofsemiconductor chips each with back sides and with intermediate spacesbetween them, wherein the intermediate spaces are filled with a firstlayer of plastic package molding compound and the back sides are coveredwith a second layer of plastic package molding compound.
 21. The panelof claim 20, wherein the plastic package molding compound of the firstlayer in an uncrosslinked state has a lower viscosity than the secondlayer.
 22. The panel of claim 20, wherein the viscosities of the firstand second layers in an uncrosslinked state differ in such a way thatthe viscosity of the first layer is lower by at least an order ofmagnitude than the viscosity of the second layer.
 23. The panel of claim20, wherein the plastic package molding compound of the first layer isadapted to application in the intermediate spaces.
 24. The panel ofclaim 20, wherein the plastic package molding compound of the secondlayer is adapted to application over the back sides.
 25. The panel ofclaim 20, wherein the first and second layers are produced by means ofhigh-pressure injection-molding processes.
 26. The panel of claim 20,wherein the first and second layers are produced by means of vacuumprinting processes.
 27. A method for producing a panel from a leadframefor a number of electronic components in corresponding componentpositions with semiconductor chips, which are encapsulated by two layersof a plastic package molding compound, comprising: providing a leadframewith a number of component positions that have a bonding channel openingat their center; applying a double-sided adhesive film with a bondingchannel opening in the component positions; applying semiconductor chipswith their active upper sides to the double-sided adhesive film;introducing bonding connections in every bonding channel forelectrically connecting contact areas of the semiconductor chip toexternal contacts on an underside of the leadframe; filling the bondingchannel with a plastic covering compound; printing a first layer oflow-viscosity plastic package molding compound onto back sides of thesemiconductor chips for filling intermediate spaces betweensemiconductor chips on the leadframe; printing on a second layer ofhigh-viscosity plastic package molding compound for covering the backsides of the semiconductor chips; curing the plastic package moldingcompound to form a closed upper side of the panel; and applying externalcontacts to an underside of the panel.
 28. The method of claim 27,wherein printing on the first and second layers of low-viscosity andhigh-viscosity plastic package molding compound takes place by means ofscreen printing.
 29. The method of claim 27, wherein a spatula ispressed under pressure on to a printing screen when printing on thefirst and second layers of low-viscosity and high-viscosity plasticpackage molding compound.
 30. The method of claim 27, wherein thedifference in the viscosity of low-viscosity and high-viscosity plasticpackage molding compound is set to at least an order of magnitude. 31.The method of claims 27, wherein the second layer of plastic packagemolding compound is applied with the same printing screen as the firstlayer of plastic package molding compound.
 32. The method of claim 27,wherein the panel is divided into individual electronic components inorder to produce an electronic component.